Adult body size measurement redundancies in Osmia lignaria and Megachile rotundata (Hymenoptera: Megachilidae)

Authors: McCabe, Lindsie; BOYLE, NATALIE - Pennsylvania State University; SCALICI, M - Utah State University; Pitts Singer, Theresa

Submitted to: PeerJ
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2021
Publication Date: 11/2/2021
Citation: McCabe, L.M., Boyle, N.K., Scalici, M.B., Pitts Singer, T. 2021. Adult body size measurement redundancies in Osmia lignaria and Megachile rotundata (Hymenoptera: Megachilidae). PeerJ. 9. Article e12344. https://doi.org/10.7717/peerj.12344.
DOI: https://doi.org/10.7717/peerj.12344

Interpretive Summary: Bee body size estimates are frequently used in ecological and agricultural studies to better understand aspects of behavior, reproduction, and survival. However, metrics that estimate size have included both body mass and unique body measurements, such as the width of the head and distance between the points of wing attachments. For some studies, it is important to know both body size and weight as separate measures, but the relationships and possible redundancies in these measurements have not been robustly examined. Here, we determined the relationships between commonly used metrics for two commercially managed solitary bees, the blue orchard bee and the alfalfa leafcutting bee. We obtained measurements from newly emerged adult bees and statistically modeled relationships. For leafcutting bees, and found that wing spacing increased in a linear fashion with head width, fresh weight, and dry weight, and that head width increased linearly with fresh and dry weight. Similar measurement relationships were found for blue orchard bees, except that wing spacing and head width each had exponential relationships with fresh weight. For both species, the strongest model patterns were found when both males and females were combined, rather than separated by sex. The results of this analysis can simplify evaluations of these two managed species’ responses to different artificial or environmental variables by knowing that only one metric is needed for reliably estimating size.

Technical Abstract: Metrics to estimate bee body size have included both mass and morphometrics, such as head capsule width (HCW) and intertegular distance (ITD). However, the relationships and possible redundancies of such measurements have not been widely examined. We determined relationships between commonly used metrics for managed solitary bees, Osmia lignaria and Megachile rotundata. We measured newly emerged adults and modelled relationships. We found: 1) a linear relationship between all metrics except the relationship between O. lignaria ITD and fresh weight and HCW and fresh weight, 2) an exponential relationship between ITD and HCW when correlated with fresh weight for O. lignaria, and 3) for both species, the strongest fits to models when males and females were pooled, rather than separated. Depending on the study question, knowing that only one metric may be needed for reliably estimating size can simplify evaluations of O. lignaria and M. rotundata responses to artificial or environmental variables.